1. Field of the Invention
The present invention relates to a method for driving a liquid crystal display device assembly including a liquid crystal device and a planar light source device.
2. Description of the Related Art
In liquid crystal display devices, a liquid crystal material does not emit light by itself. Instead, a direct-lighting-type planar light source device (backlight) is disposed at the back surface of a liquid crystal display device to emit light. In color liquid crystal display devices, one pixel is formed of three sub-pixels, such as a red (R) light-emitting sub-pixel, a green (G) light-emitting sub-pixel, and a blue (B) light-emitting sub-pixel. Then, by operating a liquid crystal cell forming one pixel or one sub-pixel as one type of optical shutter (light valve), i.e., by controlling the light transmittance (aperture ratio) of each pixel or each sub-pixel, the amount (ratio) of illumination light (for example, white light) emitted from the planar light source device and passing through the pixel or sub-pixel can be controlled so that images can be displayed. With the recent increase in the size of liquid crystal display devices, planar light source devices have also increased in size.
A known planar light source device illuminates the overall display area of a liquid crystal display device with a uniform and constant level of brightness. Another type of planar light source device is also known from, for example, Japanese Unexamined Patent Application Publication Nos. 2004-212503 and 2004-246117. The planar light source device disclosed in such publications includes a plurality of planar light source units corresponding to a plurality of display area units forming the overall display area of a liquid crystal display device, and controls the light emission conditions of the planar light source units to change the distribution of the illuminations in the display area units.
Basically, the above-described planar light source device is controlled according to the following method. It should be noted that a signal is externally input into a drive circuit and, based on this input signal, a control signal is generated for each pixel for controlling the light transmittance of the pixel and is supplied to the pixel from the drive circuit. It is now assumed that the maximum luminance of each planar light source unit forming the planar light source device is indicated by Ymax, the maximum light transmittance (aperture ratio) (more specifically, for example, 100%) of the pixels forming each display area unit is indicated by Ltmax, and the light transmittance (aperture ratio) of each pixel for obtaining the luminance of the display area (hereinafter may be referred to as the “display luminance y”) when each planar light source unit exhibits the maximum luminance Ymax is indicated by Lt. In this specification, the display luminance y obtained by the light source luminance Y and the light transmittance Lt can be expressed by the following equation (A) using an operator **.y=Y**Lt   (A)
In this case, the light source luminance Y of each planar light source unit forming the planar light source device should be controlled to satisfy the following equation.Y**Ltmax=Ymax**LtThe concept of the above-described control method is shown in FIGS. 28A and 28B. In this case, the light source luminance Y of the planar light source unit is changed for each frame for displaying an image (which is referred to as an “image display frame”) on the liquid crystal display device.